In vitro Model Systems for Studies Into Retinal Neuroprotection

Abstract

Therapy development for neurodegenerative diseases of the retina constitutes a major unmet medical need, and this may be particularly relevant for inherited diseases of the retina, which are largely untreatable to this day. Therapy development necessitates appropriate models to improve the understanding of the underlying degenerative mechanisms, as well as for the testing and evaluation of novel treatment approaches. This review provides an overview of various in vitro model systems used to study retinal neuroprotection. The in vitro methods and technologies discussed range from primary retinal cell cultures and cell lines, to retinal organoids and organotypic retinal explants, to the cultivation of whole eyeballs. The advantages and disadvantages of these methods are compared and evaluated, also in view of the 3R principles (i.e., the refinement, reduction, and replacement of live animal testing), to identify suitable in vitro alternatives for in vivo experimentation. The article further expands on the use of in vitro models to test and evaluate neuroprotective treatments and to aid the development of retinal drug delivery systems. Among the pharmacological agents tested and characterized in vitro are such that interfere with aberrant cyclic guanosine monophosphate (cGMP) -signaling or such that inhibit the activities of poly (ADP-ribose) polymerase (PARP), histone deacetylases (HDAC), calpain-type proteases, as well as unfolded protein response-related stress. We then introduce nanoparticle-based drug delivery systems and discuss how different in vitro systems may be used to assess their efficacy in the treatment of retinal diseases. The summary provides a brief comparison of available in vitro models and relates their advantages and limitations to the various experimental requirements, for instance, for studies into disease mechanisms, novel treatments, or retinal toxicity. In many cases, combinations of different in vitro models may be required to obtain a comprehensive view of the efficacy of a given retinal neuroprotection approach.

An Ex Vivo Electroretinographic Apparatus for the mL-Scale Testing of Drugs to One Day and Beyond

“…Major efforts are under way to establish good in vitro and ex vivo alternatives to the in vivo retina, one major aim being faster and cheaper development of therapies for ocular diseases. In vitro technologies are at various levels of maturity, such as primary retinal cell cultures, retina-derived cell lines, retinal organoids, retinas-on-a-chip and bioprinted retinas [20,37]. Important advances were also made in the long term organotypic culture of retinal explants [20,32,36].…”

“…In vitro technologies are at various levels of maturity, such as primary retinal cell cultures, retina-derived cell lines, retinal organoids, retinas-on-a-chip and bioprinted retinas [20,37]. Important advances were also made in the long term organotypic culture of retinal explants [20,32,36]. All these models offer direct pharmacological access and, potentially, longitudinal monitoring of effects, but lack the expression of the physiological light responses generated by in vivo or acutely isolated retinas.…”

“…By 'chronically', we mean being able to continuously monitor light responses beyond the few hours mentioned in previous mammalian studies at body temperature [3,9,14,15], studies that in all cases employed active superfusion. This would enable more demanding tests such as characterizing slow drug release from nano-devices or, if several days could be reached, even screen the effects of therapeutic molecules on fast-progressing models of inherited retinal degeneration [20]. Our main other design requirements were: (i) volume of the bathing medium on the mL scale; (ii) retinas fully immersed to ensure a good exposure to test solutions; (iii) test drugs easy to add during an experiment without major environmental perturbations; (iv) multiple pairs of retinas recorded concurrently.…”

A treatment within sight: challenges in the development of stem cell-derived photoreceptor therapies for retinal degenerative diseases

“…Retinal organoids have since emerged as valuable tools for the investigation of retinal development ( 106 ) and diseases in vitro ( 107 ), therapeutic drug screening ( 108 ), exploration of gene therapies ( 109 ), and evaluation of neuroprotective agents ( 110 ). Furthermore, retinal organoid technologies have reached human trials to treat RP ( 111 ).…”